IDEAL FERTILIZERS 79 



poisonous fluid, created by the action of the fungus will 

 cause further death and decay until there is practically 

 no difference in its effect and the effect of the fungus 

 first mentioned except it must have a point for entrance. 

 Citrus "withertip" and lettuce "drop" are common ex- 

 amples of the third class. In the fourth class are the 

 "damping-off" fungi, of which there are several varieties. 

 These live on decayed matter in the soil, but they are 

 more virulent than those preceding, as they can attack 

 perfectly healthy young seedlings of many plants. They 

 ente? the stalk at or near the surface of the ground, either 

 starting decay there at once or clogging the water pas- 

 sages so the top of the plant wilts and topples over, after 

 which decay rapidly sets in. Whole seed beds are thus 

 attacked so suddenly that often the grower can do noth- 

 ing to save his plants after the trouble first appears; 

 therefore he should guard against it. Land known to be 

 subject to damping-off should not be used for a seed-bed. 

 Seed-beds should always be well drained and the soil 

 kept aerated by constant stirring. Dry sulphur sprinkled 

 on the surface and lightly scratched in is a good pre- 

 ventive. A spray of weak ammoniacal copper carbonate 

 solution is also effective if given in time. 



Bacteria differ from fungi in that they live wholly 

 within their host, clogging the passages and thereby pro- 

 ducing death and decay. Since they are entirely within 

 the plant, spraying is ineffective. The entrance is often 

 made through tender roots and the disease carried over 

 the field by the feeding of insects from plant to plant. 



